The present invention relates to a method of manufacture of a composite material including reinforcing material such as fibers or whiskers or the like within a matrix of matrix metal, and more particularly relates to a method of manufacture of such a composite material utilizing a pressurized casting method in which the contact between the matrix metal and the reinforcing material is improved.
One per se well known set of methods of making composite materials of the above mentioned kind are the so called pressurized casting methods, in which the matrix metal is infiltrated into the interstices of the finely divided reinforcing material in the molten state under pressure. Such, for instance, are the high pressure casting method, the centrifugal casting method, the die casting method, the low pressure casting method, and the autoclave method. In particular, in the case of the high pressure casting method, the reinforcing material is inserted into a mold cavity of a casting mold, molten matrix metal is poured into said mold cavity onto the reinforcing material, and then pressure is applied to the matrix metal which is solidified while being kept under such pressure.
Now, in this high pressure casting method, it is a prior art concept, as proposed in Japanese Patent Application No. Sho 55-107040 (1980), for the reinforcing material to be preheated to a temperature of at least the melting point of the matrix metal, and to be maintained at that preheated temperature as the molten matrix metal is introduced into the casting mold. This preheating aids the penetration of the molten matrix metal into the interstices between the fibers, whiskers, particles, or the like of the reinforcing material, and is very helpful for producing a good quality composite material with good adhesion between the matrix metal and the reinforcing material. However, performing this preheating has the disadvantages of utilization of much energy, and also is quite troublesome with regard to handling.
Further, in this high pressure casting method, it is also a prior art concept, as proposed in Japanese Patent Application No. Sho 56-132538 (1981), for the reinforcing material to be formed into a body of a definite and quite sturdy shape in advance, before being inserted into the cavity of the casting mold. This is done in order to keep the reinforcing material fixed in a desired density, shape, and orientation during the high pressure casting process without the use of any particular special means for holding it in position in the casting mold. The concept is also well known for this forming of the reinforcing material into a formed mass in advance to be done by bonding together the fibers, whiskers, particles, or the like of the reinforcing material by the use of an inorganic binder, such as silica: a mass of the reinforcing material formed into the desired shape is steeped in an aqueous sol or the like containing the inorganic binder, and is then dried, so that the inorganic binder sticks the fibers or the like of the mass securely together. This method is very effective for ensuring that the reinforcing material is kept fixed in a desired density, shape, and orientation during the high pressure casting process; but because some of the inorganic binder remains around the fibers or the like of the reinforcing material after infiltration by the molten matrix metal, even if as described above preheating of the reinforcing material mass to a temperature equal to or higher than the melting point of the matrix metal is carried out, the contact and adhesion between the reinforcing material and the matrix metal may be deteriorated, and it is not always assured that a composite reinforced material of a high quality is produced.